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PDGF ( c-sis of Simian Sarcoma)

PDGF ( c-sis of Simian Sarcoma). Dermatofibrosarcoma. Simian Sarcoma Virus (SSV). SSV- transforming retrovirus found in the wooly monkey Transforming gene- v-sis Homolog in humans- first deemed c-sis, located on chromosome 22

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PDGF ( c-sis of Simian Sarcoma)

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  1. PDGF(c-sis of Simian Sarcoma) Dermatofibrosarcoma

  2. Simian Sarcoma Virus (SSV) • SSV- transforming retrovirus found in the wooly monkey • Transforming gene- v-sis • Homolog in humans- first deemed c-sis, located on chromosome 22 • Sequencing of region indicated close similarities to the mitogen PDGF

  3. PDGF Protein • PDGF is a family of proteins, and subunits A through D have been identified • This presentation concerned with A and B, but mostly PDGFB • Biologically active PDGF are homo and heterodimers; these dimers are assembled intracellularly

  4. PDGF Protein • Control of biosynthesis/secretion occurs on several levels • Transcription • Post transcription • Proteolytic processing • Availability depends on association with extracellular matrix proteins

  5. Biology of PDGFB • PDGFB is sufficient for mitogenesis • Different dimers stimulate different receptors- varies the cellular effect • Necessary for embyogenesis, while other subunits are not

  6. Knockout Mice • Mice lacking the PDGFB gene are thus far identical to mice lacking PDGFRB • These knockouts die during late gestation from cardiovascular complications- issues ranging from glomeruli function in kidneys, to cardiac muscle malfunction • In embryos, highest expression is sprouting, immature, capillary endothelium and endothelium of growing arteries

  7. PDGF Pathway • The dimerized PDGF ligands bind to cell surface receptor tyrosine kinases • These subsequently form homo or heterodimers of a and b subunits and auto-phosphorylate • Activated receptors interact with SH2 domains of several proteins and initiate many pathways • Including: PLCg, PI3K, SHP2 phosphatase, and Src family kinases • These converge on a set of immediate early genes

  8. Heldin, et al

  9. Cellular Response to PDGF

  10. Firm, hyperpigmented dermal, subcutaneous nodules that grow slowly Most often found on trunk of body Commonly recur after standard surgery 30-40% of the time Uncontrolled division of fibroblasts Fibroblasts produce collagen 1A, and also contain PDGF receptors DFSP tissues express fusion protein COL1A1/PDGFB Dermatofibrosarcoma Protuberans (DFSP)

  11. Fusion of Col1A1 Deregulates PDGFB • In DFSP tissue cells, often supernumerary rings and translocations are present which place the PDGFBgene under control of collagen 1 A promoter sequences • The resulting chimeric protein lacks the regulatory subunit of PDGFB, located in exon 1 of normal PDGFB • High levels of conservation occur in the PDGF segment of the chimeric protein, while COL1A1 sequences differ greatly across cell lines • Implications??

  12. Karyotype of DFSP Cell Pedeutour et al. 1994

  13. Chimeric Protein Wang et al, 1999

  14. Future in DFSP • Diagnostic: Reverse transcriptase polymerase chain reaction (RT-PCR) detects COL1A1/PDGFB chimeric mRNA, and can be used to determine if a tumor is DFSP • Treatment: PDGF tyrosine kinase inhibitor has been suggested as drug therapy; ST1571 (imatinib) • Clinical trials still underway to test effectiveness, but much research is in progress

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